noise=randn(1,10000);
y=filter(b,a,noise);
Fd=44.2e6;
Td=1/Fd;
T=Td*length(noise);
t=0:Td:(T-Td);
f=0:1/T:(Fd-1/T);
Sf=fft(y);

stem(f,abs(Sf));
